urlprotocol: receive a list of protocols from the caller

This way, the decisions about which protocols are available for use in
any given situations can be delegated to the caller.

libavformat/gopher.c

@@ -94,7 +94,7 @@ static int gopher_open(URLContext *h, const char *uri, int flags)
 
     s->hd = NULL;
     err = ffurl_open(&s->hd, buf, AVIO_FLAG_READ_WRITE,
-                     &h->interrupt_callback, NULL);
+                     &h->interrupt_callback, NULL, h->protocols);
     if (err < 0)
         goto fail;